FRIDAY, March 30 (HealthDay News) -- Nearly two-thirds of American children with autism have been bullied at some point in their lives, and these kids are bullied three times more often than their siblings without autism, a new survey finds.

Bullying occurs in every grade but is worst in grades five through eight, with 42 percent to 49 percent of autistic children in those grades bullied, according to the survey of nearly 1,200 parents of autistic children ages 6 to 15.

The Interactive Autism Network (IAN), a project of the Kennedy Krieger Institute, conducted the survey.

"These survey results show the urgent need to increase awareness, influence school policies and provide families and children with effective strategies for dealing with bullying," Paul Law, director of the IAN Project, said in an institute news release.

Children with autism, a developmental disorder, usually have delayed language development and difficulty with social interaction.

"Children with [autism] are already vulnerable. To experience teasing, taunts, ostracism or other forms of spite may make a child who was already struggling to cope become completely unable to function," Law said. "The issue is complex and we plan to carefully analyze the data and publish peer-reviewed findings that will serve to advance policy and care for individuals with [autism]."

Children with autism in public schools are bullied nearly 50 percent more often than those in private schools or special-education schools, the researchers found.

Types of bullying experienced by autistic children include: being teased, picked on or made fun of (73 percent); being ignored or left out of things on purpose (51 percent); being called bad names (47 percent); and being pushed, shoved, hit, slapped or kicked (30 percent).

Bullying is experienced by 57 percent of children with autism who want to interact with others but have difficulty making friends, compared with 25 percent of those who prefer to play alone and 34 percent of those who will play with others only if approached.

Fifty-two percent of the parents said their child had been taunted by other children in order to trigger a meltdown or aggressive outburst.

Kids with Asperger's syndrome, a high-functioning type of autism, were nearly twice as likely as children with another autism disorder to be bullied, perhaps because of different school placements, the researchers said.